I know, of course, that you can work on open source projects (or startups! :P ), but this usually requires a larger investment of time. I also know of:

1) The "Six hour startup" project, for first-world meetups in the Seattle area

2) http://justhackit.slinkset.com/ (which I heard about on HN)

But the first one is a model for real-world meetups only, and the second one doesn't seem to have much momentum, and seems more designed towards one-time projects for which you're seeking a partner or two. I'm more specifically speaking of something which would propose new, small projects rather regularly.

Have you heard of something similar? Here's the thread on Reddit for more details of our ideas:

http://www.reddit.com/r/programming/comments/7shvy/q_is_there_a_good_site_for_complementary_skills/c07a5hg